Patent Documents 1-3 disclose brake systems each including (i) a hydraulic friction brake device configured to restrict wheel rotation by causing a frictional engagement member to be pressed against a brake rotary body by hydraulic pressure of a brake cylinder and (ii) an electric friction brake device configured to restrict wheel rotation by causing a frictional engagement member to be pressed against a brake rotary body by drive force of an electric motor that serves as a brake motor.
In the brake system disclosed in Patent Document 2, the electric friction brake device and the hydraulic friction brake device are both provided for each front wheel while the electric friction brake device is provided for each rear wheel. The hydraulic friction brake device provided for each front wheel is activated by hydraulic pressure of a master cylinder, and braking force of the electric friction brake device is controlled such that a sum of braking forces of the hydraulic friction brake device and electric friction brake device becomes close to a target value that is determined depending on an operational state of a brake operating member operated by a vehicle driver.
In the brake system disclosed in Patent Document 3, electric energy acquired in an electric motor (referred to as a regenerative motor) that is connected to each wheel is directly supplied to a brake motor of the electric friction brake device or returned to a battery. That is, the electric energy is suppliable to the brake motor from the regenerative motor or from the battery. When the supply of the electric energy from the regenerative motor to the brake motor is insufficient, the electric energy is supplied from the battery to the brake motor.